Arrangement in axial fans for the transport of dust commingled gases



June 1954 H. LJUNGSTRGM 3,139,310

ARRANGEMENT IN AXIAL FANS FOR THE TRANSPORT OF DUST COMMINGLED GASES Filed Dec. 31, 1962 5 Sheets-Sheet 1 FIG. I.

mvsu'gonz HERBERT LJUNGSTROM ATTYS.

June 30, 1964 H. LJUNGSTRGM 3,139,310

ARRANGEMENT IN AXIAL FANS FOR THE TRANSPORT OF DUST COMMINGLED GASES Filed Dec. 31, 1962 3 Sheets-Sheet 2 FIG.2. T

mvEN-rpa; HERBERT LJUNGSTROM ATTYS- June 30, 1964 H. LJUNGSTRGM 3,139,310

ARRANGEMENT IN AXIAL FANS FOR THE TRANSPORT OF DUST COMMIQGLED GASES 3 Sheets-Sheet 3 Filed Dec. 31, 1962 FIGB.

FIG

INVEN'QOR? HERBERT LJUNGSTROM ATTYS United States Patent The present invention relates to axial fans used for the transport of dust commingled gases and more specifically to axial fans which have adjustable blades.

In axial fans intended for transporting dust commingled gases, there is always a risk of dust depositing on the outer portions of the fan hub, especially at the base of the fan blades and in the spaces around the base plates of the blades. Not only do such deposits complicate and eventually jeopardize the adjustment of the blades, they also contribute to the rise of corrosion as the dust generally is hygroscopic and tends to absorb any moisture existing in the gas. In cases when the gas has a low dew-point the absorption of moisture may further increase through condensation caused by contact of the gas with the cold fan hub.

A principal object of the present invention is to eliminate the afore-mentioned drawbacks in a simple and effective way. In the present embodiment of the invention, the cuts for the base plates of the blades are made with such dimensions that a circular slot is formed between the base plates and the hub body, and that means are available to provide the slots with scavenging air which may be treated by preheating.

In a suitable embodiment of the invention, a pressure chamber is located on the admission side of the fan wheel formed between the fan hub and a hub cap tight against the fan hub. The pressure chamber is connected to a pipe for the supply of scavenging air and by means of a number of holes bored in the fan hub, communicates with the slots around the base plates of the fan blades.

In accordance with another embodiment of the invention, the scavenging air may also be supplied in such a way that the fan hub is made with a closed pressure chamber. In this embodiment the axles of the fan blades are made hollow to allow communication between the pressure chamber and said circular slots around the base plates of the fan blades.

By providing a relatively small amount of air, for instance corresponding to 12% of the amount of gas carried by the fan, and allowing the air to discharge at a high speed over the parts most exposed to dust deposits, the harmful dust deposits may be entirely prevented and the above-mentioned drawbacks thereby eliminated. In instances where there is a risk of condensation, the scavenging air is preheated before being supplied to the fan. However, in other cases it may be advantageous to supply cold scavenging air, which when utilized in the embodiment of the invention having hollow axles for the fan blades may also serve the dual function of cooling the axles and the bushings for the fan blades.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings in which:

FIG. 1 is a vertical sectional view of an axial fan embodying the present invention;

FIG. 2 is a sectional view of a portion of the fan shown in FIG. 1, enlarged to illustrate the mechanism by which the pitch of the blades is adjusted;

FIG. 3 is a side elevation taken along line 33 of FIG. 2 having portions broken away to more clearly illustrate the means for adjusting the pitch of the blades;

Wee"

FIG. 4 is an enlarged vertical sectional view of a portion of an axial fan illustrating another embodiment of the invention; and

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4.

In the drawings, a fan wheel 1, of the axial type, is journalled on an axle 2 and built into a casing 3. The fan wheel is made with adjustable-pitch blades 4, each of which are provided with an axle 6 which is journalled in a radially extending, concentric fan hub 5, and fixed in a base plate 7, countersunk in the hub. The adjustment of the fan blades is shown and discussed fully in the Dagrell Patent No. 3,085,631, but will be briefly discussed hereinafter. I

The fan blades are rotatably adjustable with the aid of an adjustment means comprising an adjustment disc 40 which may be axially displaced thereby causing movement of crank levers 41 which are connected to the axles 6 of the blades 4. The adjustment disc 40 is rotated on an axle 42 which is mounted coaxially with the fan axle 2. The axle 42 may be displaced axially by adjustment of a connecting member 10, and externally adjustable cooperating linkages 8 and 9. In front of and behind the fan wheel are arranged elongated isolated hub cones 12 and 13 respectively. In accordance with the invention the cuts in the fan hub 5 for the base plates of the blades are made with such dimensions, that a restricted annular slot or passageway 14 is formed between each base plate and its associated hub body. This slot communicates with scavenging air means comprising a pressure chamber 16, located on the admission side of the fan wheel by means of a number of bored holes 15 in the fan hub. The pressure chamber 16, in the illustrated embodiment, is formed between the fan hub and a hub cap 17 which tightens against the fan hub. The pressure chamber 16 is connected to air supply means comprising a pipe line 18 which connects to a fan 19 which is of sufficient size to supply the required amount of scavenging air at suitable pressure. In certain cases the air supply means may be dispensed with, as the fan wheel itself, under certain load conditions produces sufiicient underpressure for the supply of the required amount of scavenging air. As illustrated in FIG. 1, there is a heating unit 20 connected in the pipe line 18 for heating the scavenging air as well as a filter or air cleaner 21 for cleaning the air. The quantity of the supplied scavenging air may be adjusted by means of a throttle valve 22, mounted in the pipe line 18.

The drawing shows only an exemplified embodiment of an axial fan in accordance with the invention, and the details for the supply of the scavenging air may of course be varied in many ways within the scope of the invention. For example, as illustrated in FIGS. 4 and 5 the axles 6a may be made hollow, the inner end of which may be communicative with the pressure chamber 16a through the slots 30 while the upper ends of the hollow axles 6a may communicate with the annular slot 14a by way of slots 31 formed between the base plate 7a and the fan hub 5a.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be made without departing from the spirit and the scope of the invention as hereinafter claimed.

What I claim is:

1. An axial fan for transporting dust-laden gases comprising a radially-extending concentric hub mounted on a rotatable shaft, a plurality of adjustable-pitch fan blades disposed about the periphery of said hub, said hub having recesses about its periphery, a circular base plate and rotatable axle mounting each of said blades intermediate a recess in said hub and said blades, adjustment means connected to said rotatable axles to cause changes in pitch of said blades, said recesses having a larger diameter than said base plates and spaced therefrom to define annular slots circumscribing each of said base plates, and scavenging air means connecting to said hub and communicative with at least some of said annular slots to supply a gaseous medium through said slots at a velocity sufficient to prevent dust buildup in said slots.

2. An axial fan for transporting dust-laden gases in accordance with claim 1 wherein said scavenging air means includes a stationary hub-cap mounted on the inlet side of said fan having a portion spaced from said hub so as to define a closed pressure chamber therebetween, gaseous medium inlet means connected to said hub-cap for supplying said medium to said pressure chamber, means defining a plurality of passageways in said hub between said annular slots and said pressure chamber providing communication of gaseous medium between said pressure chamber and said annular slots.

3. An axial fan for transporting dust-laden gases in accordance with claim 2 wherein said gaseous medium inlet means includes means for preheating said gaseous 4- medium prior to entry of said medium into said pressure chamber.

4. An axial fan in accordance with claim 1 wherein said rotatable axles are hollow and wherein said scavenging air means includes a stationary hub-cap mounted on the inlet side of said fan having a portion spaced from said hub so as to define a closed pressure chamber therebetween, gaseous medium inlet means connected to said hub cap for supplying said medium to said pressure chamber, means defining passageways in said hub and said rotatable axles providing gaseous communication between said pres sure chamber and said axles, and means defining holes between said axles and said annular slots providing gaseous communication therebetween.

References fited in the file of this patent UNITED STATES PATENTS 2,599,470 Meyer June 3, 1952 2,630,965 Greatrex et al Mar. 10, 1953 2,656,147 Brownhill et a1. Oct. 20, 1953 2,858,102 Bloomberg Oct. 28, 1958 2,981,463 Dagrell Apr. 25, 1961 

1. AN AXIAL FAN FOR TRANSPORTING DUST-LADEN GASES COMPRISING A RADIALLY-EXTENDING CONCENTRIC HUB MOUNTED ON A ROTATABLE SHAFT, A PLURALITY OF ADJUSTABLE-PITCH FAN BLADES DISPOSED ABOUT THE PERIPHERY OF SAID HUB, SAID HUB HAVING RECESSES ABOUT ITS PERIPHERY, A CIRCULAR BASE PLATE AND ROTATABLE AXLE MOUNTING EACH OF SAID BLADES INTERMEDIATE A RECESS IN SAID HUB AND SAID BLADES, ADJUSTMENT MEANS CONNECTED TO SAID ROTATABLE AXLES TO CAUSE CHANGES IN PITCH OF SAID BLADES, SAID RECESSES HAVING A LARGER DIAMETER THAN SAID BASE PLATES AND SPACED THEREFORM TO DEFINE ANNULAR SLOTS CIRCUMSCRIBING EACH OF SAID BASE PLATES, AND SCAVENGING AIR MEANS CONNECTING TO SAID HUB AND COMMUNICATIVE WITH AT LEAST SOME OF SAID ANNULAR SLOTS TO SUPPLY A GASEOUS MEDIUM THROUGH SAID SLOTS AT A VELOCITY SUFFICIENT TO PREVENT DUST BUILDUP IN SAID SLOTS. 